Sodium dithionite stabilization against self-ignition

ABSTRACT

To retard self-ignition of commercial grades of sodium dithionite when contacted with moisture and/or water, small but effective amounts of low concentration alkali metal and ammonium salts of diglycolic acid are added, said additive salts being beneficial to bleaching processes in which sodium dithionite may be used, while at the same time avoiding eutrophication of lakes and streams into which the bleaching effluent may ultimately flow.

United States Patent [1 1 Ellis et al.

[ Feb. 26, 1974 SODIUM DITI'IIONITE STABILIZATION AGAINST SELF-IGNITION [751 lnventors: Leonard C. Ellis, Chesapeake;

Mearl A. Kise, Portsmouth, both of Va.

[73] Assignee: Virginia Chemicals Inc.,

Portsmouth, Va.

[22] Filed: July 26, 1972 [21] Appll No; 275,448

[521 US. Cl 423/515, 252/105, 252/188,

8/110 [51] Int. Cl ..C01b 17/98 [58] Field of Search. 252/188, 105; 423/515; 8/110 [56] References Cited UNITED STATES PATENTS 7/1950 Hurd et a1 1, 252/188 9/1962 Franklin et a1. 252/188 3,353,909 11/1967 .lanson et a1. 423/515 3,433,590 3/1969 van Damme-van Weele 252/1811 3,468,623 9/1969 van Damme-van Weele 252/188 3,645,665 2/1972 Etters l l l 252/188 3,672,829 6/1972 Kise et a1. 252/188 Primary Examiner-Carl D. Quarforth Assistant Examiner-lrwin Gluck Attorney, Agent, or Firm-J. Gibson Semmes [57] ABSTRACT 14 Claims, No Drawings SODIUM DlTl-IIONITE STABILIZATION AGAINST SELF-IGNITION BACKGROUND OF INVENTION Under normal storage conditions, commercial grades of sodium dithionite can be held without appreciable decomposition for several years, if kept dry. There have been reports, however, of instances where sodium dithionite in storage has spontaneously ignited," i.e., decomposed with heat, resulting in considerable damage. As the result of such ignition, copious volumes of noxious sulfurous gases are evolved.

It is a well-known fact that fires" can be caused by contact of sodium dithionite with water, a combination which liberates heat. Where large quantities are confined, in drums or storage bins, sufficient heat can accumulate to reach a temperature, even with small amounts of water, to start the decomposition reaction. An explosion can occur from the internal pressure generated by the decomposition when a gas-tight storage container such as a drum is involved. Although precautions are generally taken to keep sodium dithionite dry, moisture from the air, residual moisture from the man ufacturing process, or water from accidental wetting of the stored material may initiate the decomposition reaction under certain conditions.

It has been reported that sodium dithionite decomposes and "burns" with or without the presence of moisture if the temperature is allowed to reach l35-190 C. Presently accepted stabilizers such as alkali metal carboxylates (e.g., sodium benzoatc) and watcr-soluble macro-molecules (e.g., polyethyleneimine) prevent the temperature from reaching these heights.

Known art in this field comprises the following: A. RC. Franklin and H1. Stryker, US. Pat. No. 3,054,658 (1962) to El DuPont de Nemours and C o.

B. F. Poschmann and A. .lanson, US. Pat. No.

3.287.276 (1966) to BASF.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In concentrations ranging from 0.5 to 20.0 percent by weight relative to an overall bleaching additive product of the sodium dithionite, disodium, dipotassium and diammonium diglycolate salts, have been found effective as stabilizers against self-ignition of the dry sodium dithionite when it has been contacted with moisture. In all cases herein, the grades of sodium dithionite and the diglycolate salts are within these minimums:

In the presence of 10.0 percent sodium carbonate, the blend may be protected with a 2.5 percent disodium diglycolatev Under laboratory conditions, the non-protected commercial sample of sodium dithionite reached 306 C. in 2 hours with the appearance of a flame over the surface (Table I). With 5.0 percent disodium diglycolate, the temperature reached only 133C. in 2 hours, a temperature below the thermal decomposition point of sodium dithionite. Increasing amounts of the disodium salts improved the protection. In point of fact, where 10 percent sodium carbonate was used with a 2.5 percent disodium diglycolate, the sodium dithionite was protected against self-ignition, whereas the unprotected standard having sodium carbonate alone reached a temperature of 250 C. after 2 hours.

Again, and without the sodium carbonate being added, the dipotassium salt gave evidence of protection at the 20.0 percent dipotassium diglycolate level and the diammonium salt provided protection at the 15.0 percent concentration level, all as will appear from reference to ensuing Table l.

Testing Procedure:

A 500 ml. Dewar flask (inside diameter 77 mm; depth 125 mm) was charged with 200 g. of the sodium dithionite test sample. l2 milliliters (12 ml.) of water were then pipeted rapidly around a thermocouple positioned at the center of the test sample. An additional 200 g. of sample were immediately poured on top of the initial portion and the subsequent temperature rise recorded every 2 minutes throughout the 2 hour test period.

TABLE I Sodium Hydrosulfite Self-Ignition Tests With Salts of Diglycnlic Acid Blend Na,S,O, Wt. X Na P O Wtfit. Na,CO Wt. Z SODA Wtfl KODA W15? AODA Wtfi Temp.tC.) after 2 hours 'Nit,S,O, blend was treated with 3' by weight of water in a Dewar flask. The water was placed in the middle of the blend. Disudium diglycolate. Diputussium diglycolate Diumnmnium diglycolate.

We claim:

1. A method of retarding self-ignition in dry storage of commercial grades of sodium dithionite. comprising adding to the sodium dithionite, precedent to storage, small but effective amounts of the groups alkali metal and ammonium salts of diglycolic acid.

2. The method according to claim I in which the salt comprises disodium diglycolate.

3. The method according to claim I in which the salt comprises dipotassium diglycolate.

4. The method according to claim I in which the salt comprises diammonium diglycolate.

5. The method according to claim 1 wherein the amount of additive salt is less than the sodium dithionite. the concentration ofthe additive salt being in concentration of 2.5 to 20.0 percent by weight relative to the overall product of sodium dithionite to be stored.

6. The method according to claim 2 in which the conccntration of the sodium diglycolate is at 0.5 to 20.0 percent relative to the overall product of sodium dithionite to be stored.

7. The method according to claim 3 wherein the dipotassium diglycolate is at a concentration of 3.0 to 20.0 percent. relative to the overall product of sodium dithionite to be stored.

8. The method according to claim 4 in which the ammonium diglycolate is at the concentration of 5.0 to 15.0 percent relative to the overall product of sodium dithionite to be stored.

9. The method according to claim 2 wherein sodium carbonate is added in a concentration of 10.0 percent, relative to the overall product of sodium dithionite to b e ored and the disodium diglycolate is in a concentration range of 2.5 to I00 percent relative to said sodium dithionite.

10. A bleaching agent composition of matter comprising in relative percentages by weight, the compounds:

A. dry sodium dithionite 80.0 to 99.5 percent;

B. the group alkali metal and ammonium salts of di glycolic acid 20 to 0.5 percent.

H. A bleaching agent composition of matter comprising in relative percentages by weight, the following:

A. dry sodium dithionite 99.5 to 80.0 percent; B. disodium diglycolate 05 to 20.0 percent. 12. A bleaching agent composition of matter comprising the following:

A. dry sodium dithionite 87.5 to 80.0 percent by weight; B. 10.0 percent by weight of sodium carbonate; C. 2.5 10.0 percent disodium diglycolate. 13. A composition of matter bleaching agent comprising in percentage by weight:

A. dry sodium dithionite at 97.0 80.0 percent commercial grade sodium dithionite; B. 3.0 20.0 percent dipotassium diglycolate. 14. A composition of matter bleaching agent comprising in percentage by weight:

A. 95.0 85.0 percent sodium dithionite; B. ammonium diglycolate 5.0 15.0 percent by weight. 

2. The method according to claim 1 in which the salt comprises disodium diglycolate.
 3. The method according to claim 1 in which the salt comprises dipotassium diglycolate.
 4. The method according to claim 1 in which the salt comprises diammonium diglycolate.
 5. The method according to claim 1 wherein the amount of additive salt is less than the sodium dithionite, the concentration of the additive salt being in concentration of 2.5 to 20.0 percent by weight relative to the overall product of sodium dithionite to be stored.
 6. The method according to claim 2 in which the concentration of the sodium diglycolate is at 0.5 to 20.0 percent relative to the overall product of sodium dithionite to be stored.
 7. The method according to claim 3 wherein the dipotassium diglycolate is at a concentration of 3.0 to 20.0 percent, relative to the overall product of sodium dithionite to be stored.
 8. The method according to claim 4 in which the ammonium diglycolate is at the concentration of 5.0 to 15.0 percent rElative to the overall product of sodium dithionite to be stored.
 9. The method according to claim 2 wherein sodium carbonate is added in a concentration of 10.0 percent, relative to the overall product of sodium dithionite to be stored and the disodium diglycolate is in a concentration range of 2.5 to 10.0 percent relative to said sodium dithionite.
 10. A bleaching agent composition of matter comprising in relative percentages by weight, the compounds: A. dry sodium dithionite 80.0 to 99.5 percent; B. the group alkali metal and ammonium salts of diglycolic acid 20 to 0.5 percent.
 11. A bleaching agent composition of matter comprising in relative percentages by weight, the following: A. dry sodium dithionite 99.5 to 80.0 percent; B. disodium diglycolate 0.5 to 20.0 percent.
 12. A bleaching agent composition of matter comprising the following: A. dry sodium dithionite 87.5 to 80.0 percent by weight; B. 10.0 percent by weight of sodium carbonate; C. 2.5 - 10.0 percent disodium diglycolate.
 13. A composition of matter bleaching agent comprising in percentage by weight: A. dry sodium dithionite at 97.0 - 80.0 percent commercial grade sodium dithionite; B. 3.0 - 20.0 percent dipotassium diglycolate.
 14. A composition of matter bleaching agent comprising in percentage by weight: A. 95.0 - 85.0 percent sodium dithionite; B. ammonium diglycolate 5.0 - 15.0 percent by weight. 